The present invention relates to a novel classification screen or sieve. More specifically, the present invention covers a novel classification screen, which is understood to be any device capable of classifying according to size any object passing through it, thus dividing the object material into two groups. These two groups comprise a group whose grain-size permits the material to pass through the device, and another group whose size prevents the material from passing through the device, thereby establishing an operation of separating the respective material, such as, grain, stones, ore, etc.
Known screens or sieves generally consist of at least one bed arranged in general on an almost horizontal or inclined plane and subjected to a vibrational movement, usually intense, which can vary from a few hundred vibrations per minute to almost 1800 vibrations per minute, as a general rule.
This bed consists of a metallic mesh or plate perforated with a substantial number of holes passing through it, of constant size or area, which constitute the "mesh", or screening capacity of the device. For each bed, it is customary to provide a frame or any other structural element, which is capable of sustaining said mesh, netting or perforated plate, plus the weight of the material to be classified, subjected to the dynamic vibrational action. Thus, there is known and understood as "bed", the multiple number of openings of passage contained, substantially, on a single plane.
In such known screens, it is evident that for each "bed", there are a multiple number of passage orifices which are stationary and unmovable with respect to their physical arrangement and in their passage or average diameter.
Also, such screens are integrated with others, in a cascade arrangement of a multiple number of beds, one of them collecting and classifying the material which has passed through and been classified by the bed arranged immediately above.
Such known screens are, in general, very noisy; they subject their frames and the supporting base to substantial vibrations; they cannot be adjusted except by exchanging completely the bed or mesh contained in them, and they require a powerful motor. These factors lead to relatively high installation, operating and maintenance costs--not to mention the initial cost of acquisition which is high, because, from what has been stated, these are machines which require very strong frames.
It is, therefore, an object of the present invention to construct a lighter machine, subjected to a vibrational effect of less applied force and less speed (lower frequency), the screening size of which would not be a function of a continuous layer (whether a perforated plate or sheet of metal, or a woven mesh material), which would permit the possibility of adjustments in at least part of the bed in order to alter the size of the mesh, with a markedly reduced consumption of energy, and with a well regulated selectivity of classification.